Glossary of LED Terms

Glossary of LED Terms

A

■Average Rated Life– An average rating, in hours, indicating when a percentage of a large group of lamps have failed, when operated at nominal lamp voltage and current. The life of an LED is defined as the operating time in hours for the lamp to reach L70 which designates 70% lumen maintenance (or 30% reduction in initial light output). Every lamp type has a unique mortality curve that depicts its average rated life.

B

■Binning – The separation of LEDs according to color temperature subsequent to a production run for full manufactured, distribution in terms of color, lumen output and forward voltage. This allows luminaire manufacturers to select only those LEDs that meet their acceptable performance ranges and also maintain consistency in production.

C

■Center Beam Candlepower (CBCP) –The luminous intensity at the center of the beam of a reflector lamp. Measured in candelas.

D

■Diode – A two-terminal semiconductor device having a p-n (positivenegative) junction which allows energy travel in one direction.

■Driver – A self-contained power supply that has outputs which match the electrical characteristics of the lamp. It is similar to a ballast and is used to power illumination sources.

■Heat Sink– A heat sink is an environment or object that absorbs and dissipates heat from another object. The design of an LED retrofit lamp’s heat sink is an integral factor in the overall performance of the lamp.

■High Power LED – LED chips can be assembled in two primary methods for integration in an LED retrofit lamp: SMD (Surface Mount Device) and COB (Chip on Board).

SMD – SMD LEDs are enclosed by a housing and the encased LED is soldered onto the printed circuit board (PCB). This method of assembly does not have optimal heat conduction.

COB – COB LEDs are neither encased nor connected. The LED chips are placed directly onto the PCB through wire bonding and connected to the contact surface of the PCB. The benefits of COB technology include longer life, better performance as well as higher light output due to better heat conduction in this assembly structure.

L

■LM79– An IES approved method describing procedures and precautions in performing reproducible measurements of LEDs including total flux, electrical power, efficacy (lpw) and chromaticity. This is applicable to LED products incorporating control electronics and heat sinks (LED luminaires and integrated LED sources).

■LM80 – An IES approved method for measuring lumen depreciation of solid-state (LED) light sources, array and modules. This does not apply to luminaires and does not define or provide methods for estimation of life.

P

■Power Factor (PF) – Measurement of the relationship between the AC source voltage and current. Power factors can range from 0 to 1.0, with 1.0 being ideal. Power factor is sometimes expressed as a percent. “High” power factor usually means a rating of 0.9 or greater.

T

■TM-21 – IESNA TM-21-11 provides the method for determining when the “useful lifetime” of an LED is reached, a point when the light emitted from an LED depreciates to a level where it is no longer considered adequate for a specific application through the use of extrapolated data from LM80 testing. Lumen maintenance of LED products and LED packages can vary by manufacturer. TM-21 ensures consistent lumen maintenance extrapolation methods for all LED manufacturers. TM-21 extrapolations are ‘best-case’ system lifetime estimates, and assume that no other failure mechanisms influence the life of the LED luminaire.

■Total Harmonic Distortion (THD) – A measure of the distortion of the input current on alternating current (AC) power systems caused by higher order harmonics of the fundamental frequency (60Hz in North America). THD is expressed in percent and may refer to individual electrical loads (such as ballast) or a total electrical circuit or system in a building. ANSI C82.77 recommends THD not exceed 32% for individual commercial electronic ballasts.

■Transformer – An electrical device by which the alternating current of one voltage is changed (stepped up or down) to another voltage. Magnetic transformers use a core and coil assembly transformer to start and operate the lamp. Electronic transformers operate lamps at frequencies above 20,000Hz through the use of electronic circuitry.

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